Get All DHCP Lease Info

$DHCPServer = "DHCPServer.Contoso.com";
$DHCPScopes = Get-DhcpServerv4Scope -ComputerName $DHCPServer;
foreach ($Scope in $DHCPScopes) {
Get-DhcpServerv4Lease -ComputerName $DHCPServer -ScopeID $Scope.ScopeId;
};

Change Lease Duration 30 Days, 8 Hours, 9 Minutes, 10 Seconds

Set-DhcpServerv4Scope -ComputerName $DHCPServer -ScopeID $Scope.ScopeId -LeaseDuration "30.08:09:10";